The typical hydroelectric system requires a large reservoir. At the present time, the construction of a new conventional hydroelectric system would require, for its reservoir, a large number of acres that usually are of substantial value for other purposes. Sites suitable for dam locations along a river are usually few in number and almost always would have a great impact on the overall environment if used for that purpose.
While proposals have been made to utilize tides to operate pumps for use in connection with the generation of electricity, as far as I am aware, it has never been proposed that continuously flowing water or even intermittment run-off water be used intermittently to operate a pump or a series of pumps to provide a discharge of water under a wanted head and thus eliminate the necessity of providing large reservoirs that are now required to produce a wanted operating flow and head.